la ex 2.
2x-y=1
x+y=-4 ai sistem⇒3x=-3⇒x=-3/3⇒x=-1
acum ai x=-1 si x+y=-1⇔-1+y=-4⇔y=-4+1⇒y=-3
la ex 3
3x-2mai mic decat 7⇒3xmai mic decat 7+2⇒3x mai mic decat 9⇒xmai mic decat9:3⇒x mai mic decat 3⇒x∈(-∞,3)
4-2x≤3x+14⇔-2x-3x≤14-4⇔-5x≤10⇔x≤10:(-5)⇒x≤-2⇒x∈(-∞,2]
la ex 4
6x²+0,5x=0
6x²+5/10x=0
x×(6x+5/10)=0⇒ o data x=0 si a doua oara 6x+5/10=0⇔6x=-5/10⇒x=-5/10:6⇒x=-5/10×1/6⇒x=-5/60 deci x∈{0,-5/60}
3x²+13x-10=0
Δ=b²-4ac=13²-4×3×(-10)=169+120=289
x1=-b+√Δ/2a=-13+√289/2×3=-13+17/6=4/6⇔2/3
x2=-b-√Δ/2a=-13-√289/2×3=-13-17/6=-30/6=-5
5x(5x+2)+3=2
25x²+10x+3-2=0
25x²+10x+1=0
Δb²-4ac=10²-4×25×1=100-100=0⇒x1/x2=-b/2a=-10/2×25=-10/50=-1/5
la ultima trebuie sa ma gandesc dar la ora asta nu garantez nimic :))
